<template>
    <ul class="list">
      <li class="item"
          v-for="item of letters"
          :key="item"
          :ref="item"
          @touchmove="handleTouchMove"
          @touchstart="handleTouchStart"
          @touchend="handleTouchEnd"
          @click="handleLetterClick"
        >{{item}}
      </li>
    </ul>
</template>

<script>
  export default {
    name: 'CityAlphabet',
    props: {
      cities: Object
    },
    computed: {
      letters () {
        const letters = []
        for (let i in this.cities) {
          letters.push(i)
        }
        return letters
      }
    },
    data () {
      return {
        touchStatus: false,
        startY: 0,
        timer: null
      }
    },
    updated () {
      this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
      handleLetterClick (e) {
        this.$emit('change', e.target.innerText)
      },
      handleTouchStart () {
        this.touchStatus = true
      },
      handleTouchMove (e) {
        if (this.touchStatus) {
          if (this.timer) {
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
            const touchY = e.touches[0].clientY - 79
            const index = Math.floor((touchY - this.startY) / 20)
            if (index >= 0 && index < this.letters.length) {
              this.$emit('change', this.letters[index])
            }
          }, 16)
        }
      },
      handleTouchEnd () {
        this.touchStatus = false
      }
    }
  }
</script>

<style lang="stylus" scoped>
  @import "~styles/varibles.styl"
  .list
    display flex
    flex-direction column
    justify-content center
    position absolute
    right: 0
    bottom: 0
    width: .4rem
    top: 1.58rem
    .item
      line-height .4rem
      color $bgColor
      text-align: center
</style>
